I'm using 500MHz NMR spectrometer,but the the Ar-CH2-Ar proton signals are not clear to give indication about the conformation. The rest of the peaks are ok. What may be the possible problem? Among 500, 400,300 and 200 MHz NMR spectrometer, which one is more suitable for Azocalixarenes?
First of all: is it an calix[4]arene? What exactly do you mean with „not clear“? What signal pattern is observed in the NMR spectrum? For upper rim functionalized cali[4]arenes one would not expect rapid conformational changes in any case.
Maybe you can post a picture of the spectrum? Additionally a 13C NMR should be helpful!
See: C. Jaime, J. de Mendoza, P. Prados, P. M. Nieto, C. Sanchez, J. Org. Chem. 1991, 56, 3372–3376. (DOI: 10.1021/jo00010a036)
http://pubs.acs.org/doi/abs/10.1021/jo00010a036?journalCode=joceah&quickLinkVolume=56&quickLinkPage=3372&selectedTab=citation&volume=56
it is Azo calix[4]arene (with 4 nitro aniline). In other compounds, peaks at 6.5(t) and 7.1(d) still exist with low intensity that belong to calix[4]arene and suppose to be not in product.....???
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